The therapeutic potential of "custom-made" human embryonic stem (huES) cells is widely acknowledged. However, both ethical and technical reasons stand in the way of the routine use of somatic cell nuclear transfer (SCNT) to derive genetically matched huES cells from patients. Recent progress at identifying the key molecular players involved in the maintenance of the huES cell phenotype has led to breakthrough reports describing the reprogramming of somatic cells by forcing the expression of a surprisingly manageable number of transcription factors. While these induced pluripotent stem (iPS) cells appear to be functionally identical to huES cells derived from blastocysts, the use of retroviral vectors to deliver the critical genes is still unsafe in the context of human therapies. Thus, unless alternatives to retroviral delivery are devised, iPS cells will not be clinically applicable. The specific aim of our proposal is to develop iPS cells by means of protein transduction, a technology by which recombinant proteins engineered with short cell-penetrating peptides are made available inside the cells by simply adding them to the culture medium. We postulate that protein transduction is well suited to deliver known reprogramming factors in a safe, efficient and transient manner. Our method, therefore, is designed to break existing barriers that prevent the clinical use of iPS cells. PUBLIC HEALTH RELEVANCE: Human embryonic stem (huES) cells might represent an unlimited supply of tissues for regenerative medicine. Coupled to somatic cell nuclear transfer (SCNT), huES cell technologies also opened the door to the possibility of generating tissues genetically identical to those of the donor, but the principle of this application remains to be proven in humans. In recent months, however, an approach based on the retroviral delivery of key transcription factors led to the successful reprogramming of human somatic cells into induced pluripotent stem (iPS) cells. Despite the biological significance of these findings, the resulting cells are unusable for clinical purposes, due to the risks inherent to the use of retroviral vectors. Our project will explore protein transduction as an alternative to viral delivery, with the goal of obtaining iPS cells that could be readily used for human therapeutic purposes. In this context, the proposal responds both to the general mission of the NIH and to the present Program Announcement ("Human Pluripotent Stem Cell Research Using Non-Embryonic Sources"), as it is specifically aimed at "Reprogramming human adult somatic cells to dedifferentiate into pluripotent stem cells".